Adds frameTimeMs property to Canvas3D.

Adds new performance counter called frametimeMs to Canvas3D.
This counter can be used to check how much time in milliseconds the
previous frame took from signalling paintGL to glFinish returning.
This gives insight in to how much time on average frames take to render
(excluding the presenting of the frames) and how much the frame time
varies between frames.

Change-Id: I438c33207a3835d0560521960ac71ea2f60af3d9
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@theqtcompany.com>

src/imports/qtcanvas3d/canvas3d.cpp

@@ -94,6 +94,7 @@ Canvas::Canvas(QQuickItem *parent):
     m_glContextShare(0),
     m_contextWindow(0),
     m_fps(0),
+    m_frameTimeMs(0),
     m_maxSamples(0),
     m_devicePixelRatio(1.0f),
     m_isOpenGLES2(false),
@@ -849,15 +850,29 @@ void Canvas::bindCurrentRenderTarget()
 }
 
 /*!
- * \qmlproperty uint Canvas3D::fps
+ * \qmlproperty int Canvas3D::fps
  * This property specifies the current frames per seconds, the value is calculated every
  * 500 ms.
+ * \sa frameTimeMs
  */
 uint Canvas::fps()
 {
     return m_fps;
 }
 
+/*!
+ * \qmlmethod int Canvas3D::frameTimeMs()
+ * This method returns the number of milliseconds the last rendered frame took to process. Before
+ * any frames have been rendered this method returns 0. This time is measured from the point
+ * the paintGL() signal was sent to the time glFinish() returns. This excludes the time it
+ * takes to present the frame on screen.
+ * \sa fps
+*/
+int Canvas::frameTimeMs()
+{
+    return m_frameTimeMs;
+}
+
 /*!
  * \internal
  */
@@ -929,6 +944,9 @@ void Canvas::renderNext()
     QQmlEngine *engine = QQmlEngine::contextForObject(this)->engine();
     CanvasTextureImageFactory::factory(engine)->notifyLoadedImages();
 
+    static QElapsedTimer frameTimer;
+    frameTimer.start();
+
     // Call render in QML JavaScript side
     qCDebug(canvas3drendering).nospace() << "Canvas3D::" << __FUNCTION__
                                          << " Emit paintGL() signal";
@@ -943,6 +961,8 @@ void Canvas::renderNext()
     glFlush();
     glFinish();
 
+    m_frameTimeMs = frameTimer.elapsed();
+
     // Update frames per second reading after glFinish()
     static QElapsedTimer timer;
     static int frames;

src/imports/qtcanvas3d/canvas3d_p.h

@@ -102,6 +102,7 @@ public:
     GLuint resolveMSAAFbo();
 
     uint fps();
+    Q_INVOKABLE int frameTimeMs();
 
     Q_INVOKABLE QJSValue getContext(const QString &name);
     Q_INVOKABLE QJSValue getContext(const QString &name, const QVariantMap &options);
@@ -120,6 +121,7 @@ signals:
     void contextChanged(CanvasContext *context);
     void fpsChanged(uint fps);
     void pixelSizeChanged(QSize pixelSize);
+    void frameTimeChanged(uint frametime);
 
     void initializeGL();
     void paintGL();
@@ -153,6 +155,7 @@ private:
     QQuickWindow *m_contextWindow;
 
     uint m_fps;
+    uint m_frameTimeMs;
     int m_maxSamples;
     float m_devicePixelRatio;